1. Field of the Invention
The present invention relates to a planetary gear reduction starter used for a vehicle. In particular, the present invention relates to an assembling structure for a planetary gear reduction unit.
2. Discussion of Background
FIG. 17 is a cross-sectional view showing the overall construction of an example of a conventional planetary gear reduction starter. In FIG. 17, reference numeral 1 designates the armature of a d.c. motor, numeral 2 designates a rotating shaft for the armature 1, numeral 3 designates a commutator attached to an end (on the left side in the drawing) of the armature 1, and numeral 4 designates a brush holder holding a brush, which is fixed to a rear bracket 6 by means of a bolt 5. A bearing 7 which supports a rear end portion of the rotating shaft 2 of the armature 1 is fitted to a recess formed in the rear bracket 6. A permanent magnet 8a is fixed to the inner circumferential surface of a yoke 8 in the d.c. motor and produces a magnetic field. An end of the yoke 8, which is on the side of the commutator 3, is in contact with and fitted to the rear bracket 6. The other end of the yoke, which is on the side of a rotatory output shaft 17, is connected with a front bracket 10 in which an internal gear wheel 9 constituting a planetary gear reduction device 33 is fitted to a shoulder portion 10a which is formed in the inner circumferential surface of the front bracket 10. The yoke 8 is defined from the front bracket 10 by means of a flange-like plate portion 8b which is extended inwardly in the radial direction from the other end of the yoke 8 in one piece. Hereinbelow, the term "front" with respect to any element in the planetary gear reduction starter means the right side of the element in the drawings and the term "rear" means the left side.
A projection 9i formed in the outer circumferential surface of a flange portion of the internal gear wheel 9 is fitted to the shoulder portion 10a in a recess formed in the inner circumferential surface of the front bracket 10 so that it is prevented from moving in the circumferential direction. A through bolt 32 is inserted through the rear bracket b and is engaged with a thread portion (not shown) formed in the front bracket 10. Accordingly, the internal gear wheel 9 is cramped between the shoulder portion 10a of the front bracket 10 at its one end and the plate portion 8b at its other end thereby being prevented from moving in the axial direction.
A spur gear 12 is formed at a front end portion of the rotary output shaft 2 of the armature 1. A planetary gear wheel 13 is meshed with the spur gear 12. A bearing 14 is fitted to the inner circumferential surface of the planetary gear wheel 13, and the bearing 14 is supported by a supporting pin 15. A flange 16 for firmly securing the supporting pin 15 constitutes an arm for the planetary gear reduction device 33. The arm is formed integrally with the rotary output shaft 17, which is, in turn, supported by a sleeve bearing 18 which is fitted to the inner circumferential surface of a projecting portion of the internal gear wheel 9. A sleeve bearing 19 fitted to a recess formed in rear of the spur gear 12 of the rotary output shaft 17 supports a front end portion of the rotary shaft 2 of the armature 1. Further, a steel ball 20 is disposed between the front end of the rotary shaft 2 of the armature and the rotary output shaft 17 to bear a thrust load.
A helical spline 21 is formed in an outer circumferential portion of the rotary output shaft 17, and an overrunning clutch 22 is in spline-engagement with the helical spline so as to be slidable along the axial direction. A pinion 23 is connected to the overrunning clutch 22. A stopper 24 is disposed to restrict the amount of movement of the pinion 23 in the axial direction. A sleeve bearing 25 for supporting the rotary output shaft 17 is fitted to the inner circumferential surface of an opening 10b formed at a front portion of the front bracket 10.
A lever 26 made of a resinous material is pivotally supported by the front bracket 10 wherein an end of the lever 26 is connected to a plunger 28 in an electromagnetic switch 27 and the other end is engaged with a rear portion of the overrunning clutch 22. Numeral 29 designates a lead wire for connecting the electromagnetic switch 27 to the brush 4. The other end of the lead wire is fixed to a cap 31 by means of a nut 30 on the side of the electromagnetic switch 27.
FIG. 18 shows another example of a conventional planetary gear reduction starter having a construction different from that shown in FIG. 17 wherein the same reference numerals designate the same or corresponding parts. Namely, a center plate 11 and a center bracket 34 accommodating the internal gear wheel 9 are disposed between the edge surface of an opening of the yoke 8 in a tubular form and the shoulder portion 10a of the front bracket 10 wherein a through bolt (not shown) is inserted from a closed end portion of the yoke 8 so that the planetary gear reduction device 33 is fixed in a position by engaging the through bolt with a thread portion formed in the front bracket 10.
In each of the conventional planetary gear reduction starters having the construction described above, when a key switch (not shown) is turned on, a current is passed through the electromagnetic switch 27 whereby a voltage is applied to the brush 4 through the lead wire 29 and a torque is produced in the armature 1. The rotation of the armature 1 is reduced by the planetary gear reduction device 33 and a reduced speed is transmitted to the overrunning clutch 22. On the other hand, when the electromagnetic switch 27 becomes conductive, the plunger 28 is moved in the left direction in the drawing and the movement of the plunger 28 is transmitted to the overrunning clutch 22 through the lever 26. Accordingly, the overrunning clutch 22 moves forwardly, and the pinion 23 is brought to engagement with a ring gear (not shown) on the side of the engine.
In the conventional planetary gear reduction starters, it is necessary to fasten the through bolt to the front bracket in order to fix the planetary gear reduction device. Accordingly, when there is no front bracket, it is impossible to fix the planetary gear reduction device to the yoke of the motor. However, if the front bracket can be removed and the planetary gear reduction device can be connected to the yoke, the packaging of the starters can be compact and transportation and storage of the starters by using boxes can be easy. However, there is a possibility of disconnection of the planetary gear reduction device from the yoke due to vibrations and careless handling, whereby a planetary gear wheel or a pole may come off and dust may enter into the device. This may cause a fault in an assembled product.